As part of its effort to standardize the interface of the electronic equipment, the electronic industry has established pin assignments for some of the connectors that will be used in the interface. For various computer applications, it is desirable to interconnect memory cards. The Personal Computer Memory Card International Association (PCMCIA) has established standards for interconnecting memory cards. A sixty-eight pin connector, for example, is often used. This connector has sixty signal pins, four ground return pins and four DC voltage pins, all of which are preassigned by the industry in the standards. The connectors may be through hole mounted or surface mounted. The signal to ground ratio of an electrical connector is equal to the number of signal carrying pins divided by the number of ground return pins in the connector. For the purposes of the present disclosure the DC voltage pins can be considered similar in effect to the AC voltage ground pins, thus the signal to ground ratio of the sixty-eight pin connector is 7.5 to 1.0. Typically in computer applications multiple lines are simultaneously switched and all return current generated;by this switching must be returned through one of the ground pins. The return current of eight or so signal pins, therefore, must be accommodated by a single ground pin. When the signal rise time is relatively slow, in the eight to ten nanosecond range, this presents no problem. When the rise time decreases i.e. to 1-3 nanoseconds, however, as in certain computer applications the induced voltage is increased resulting in "ground bounce" or common mode noise in the ground return pins. When the ground bounce reaches a high enough level, relative to the level of the signals, the systems may become unable to reliably read and respond to the signals thereby causing what is known in the industry as "false triggering". Since the pin assignments have been fixed by the industry, the signal to ground ratio cannot be altered. To reduce the adverse effects o the faster rise times a conductive shroud may be used to electrically interconnect the ground of the memory card to the ground of the equipment with which the card is being used.
One such shroud and a related connector are disclosed in U.S. Pat. No. 5,288,247, issued Feb. 22, 1994, to Kaufman. The shroud of the '247 patent is arranged to enclose the top of the connector and two sides thereof. A shroud for multiple connectors in a vertically Stacked relationship is disclosed in U.S. Pat. No. 5,399,105, and also owned by the present assignee. A connector and shroud assembly for use with grounded and ungrounded memory cards is disclosed in U.S. patent application Ser. No. 08/283,312, also owned by the present assignee. The connectors in the three references are top board mounted having terminal leads that are received in through holes of the circuit boards. Each of the shrouds in the above references is mounted on a board remote surface of the connector and is electrically connected to ground circuitry on a circuit board. The performance of the equipment is greatly improved by the use of such shrouds.
To achieve a more uniformed distribution and flow of current, it is generally desirable that a ground shroud include a plurality of interconnections with the circuit board ground. One way of achieving this capability with top board mounted connectors is to provide a shroud of the type that has a plate-like section extending above the formed pins at the back of the connector and a back wall having a plurality of contact sections at desired locations therealong for engaging ground circuitry on the board.
While a shroud of the type described above is suitable for top board mounted connectors having terminal members that have leads that are received in through holes on the circuit board, a problem arises when using this type of shroud with connectors having surface mounted leads. The top and back walls of the shroud prevent heat from reaching the solder paste or other material used for interconnecting the leads and circuit pads during the soldering process. Furthermore, the shroud walls prevent visual inspection of the soldered connections.
Although a two step mounting process, that is, first soldering the connector with the surface mountable leads to the board and then securing the conductive shroud to the already mounted connector and soldering the shroud to respective ground circuitry is possible; the additional manufacturing steps are not cost effective.
It is desirable, therefore, to provide a ground shroud for connectors having surface mountable leads that permits simultaneous mounting of the connector and shroud to the board and also allows visual inspection of the terminal leads after the soldering process is complete.